When adding and removing same materials to/from project repeatedly in content library, sometimes after adding the material node in navigator will display warning icon. This warning comes from editor puppet in case it has time to try to react to adding of the new node before puppet reset goes through. Typically the warning is cleared in a couple of seconds when the reset finishes, but sometimes it stays longer until user mouses over the navigator item. In rare cases puppet reset is required to get rid of the warning. In every case the warning seems invalid, since the material works fine.

The warning seems more likely to happen if you rapidly add multiple materials.